How to Find a Fault on an RCD: A Practical Guide

When an RCD trips, it usually means there is an electrical fault somewhere on the installation or with something connected to it. In some cases the problem is simple, such as a faulty appliance. In other cases it can be caused by damaged wiring, moisture, a faulty circuit, poor connections or an issue inside the consumer unit.

This guide explains the basic steps that can be taken to narrow down the cause of an RCD fault. It is written for homeowners, landlords and tenants who want to understand what may be happening before booking an electrician.

Do not remove the consumer unit cover, touch exposed wiring or bypass an RCD. If there are signs of burning, overheating, water damage, buzzing, a fishy smell or exposed conductors, stop using the affected circuit and arrange an electrician.

What an RCD Does

An RCD, or Residual Current Device, is a safety device normally found in the consumer unit. It monitors the current flowing through the electrical installation. If it detects current leaking away where it should not be, it trips and cuts the power.

That leakage can happen because of a faulty appliance, damaged cable, water ingress, poor wiring or a fault on part of the fixed installation.

Some properties have one or two RCDs protecting several circuits. Newer consumer units may have RCBOs, where each circuit has its own individual RCD protection. Finding the fault is usually easier on an RCBO board because only the affected circuit should trip.

Step 1: Check What Has Tripped

First, look at the consumer unit and identify what has turned off.

If only one switch has dropped, it may be an RCBO or circuit breaker for a single circuit.

If a wider section of the board has gone off, it may be an RCD protecting several circuits, such as sockets, lights, kitchen appliances or outdoor electrics.

Make a note of which switch has tripped. If the same RCD or circuit trips repeatedly, that gives a useful clue.

Step 2: Think About What Changed

Before resetting anything, think about what happened just before the RCD tripped.

Useful questions include:

Did it trip when a specific appliance was turned on?
Did it happen after heavy rain?
Has there been a leak or damp issue?
Has any DIY, drilling, flooring, kitchen or bathroom work been carried out?
Has a new appliance recently been plugged in?
Does it happen at the same time each day?
Does it happen when the oven, boiler, washing machine, dishwasher or shower is used?

RCD faults often follow a pattern. Finding that pattern can save time.

Step 3: Unplug Appliances on the Affected Circuit

If the RCD appears to be affecting socket circuits, unplug appliances where it is safe and practical to do so.

Common appliances that can cause RCD tripping include:

Kettles
Toasters
Washing machines
Dishwashers
Fridges and freezers
Ovens
Microwaves
Boilers
Immersion heaters
Outdoor equipment
Extension leads

Once appliances are unplugged, try resetting the RCD.

If the RCD stays on, plug the appliances back in one at a time. If it trips when one item is plugged back in or switched on, that appliance may be the cause.

If the RCD still trips with everything unplugged, the fault may be on the fixed wiring, a hard-wired appliance or the consumer unit itself.

Step 4: Check for Water or Outdoor Electrics

Water is a very common cause of RCD faults.

Outdoor lights, garden sockets, external junction boxes and pond pumps are common problem areas, especially after rain. Bathroom fans, kitchen appliances, boilers and areas around sinks can also be affected by moisture.

If the RCD only trips during or after wet weather, that is a strong sign that water may be getting into an outside fitting, cable, socket or junction box.

Do not open outdoor fittings yourself if you are not competent to do so. Isolate the affected circuit if possible and arrange proper testing.

Step 5: Reset the RCD Safely

If there is no visible damage and no signs of burning or water ingress, the RCD can usually be reset once.

If it resets and stays on, monitor it.

If it trips again immediately, do not keep forcing it back on. Repeated tripping means the fault is still present.

If the RCD will not reset even with appliances unplugged, the fault is likely to need proper electrical testing.

Step 6: Narrow Down the Circuit

On some consumer units, an RCD protects several circuits. A basic way to narrow things down is to turn off the individual circuit breakers protected by that RCD, reset the RCD, and then turn the circuits back on one at a time.

If the RCD trips when a certain circuit is turned back on, that circuit may be where the fault is.

This is only a basic indication. It does not prove the exact cause. The fault could still be a hard-wired appliance, damaged cable, damp accessory, poor connection or insulation fault on that circuit.

Do not remove covers or carry out testing unless you are competent and have the correct equipment.

Common Causes of RCD Faults

The most common causes include faulty plug-in appliances, damaged cables, damp accessories, faulty outdoor lights, water ingress, damaged sockets, old wiring, insulation resistance faults, incorrect circuit alterations and faulty RCDs.

In rental properties, the issue is often reported by the tenant as “the fuse board keeps tripping” or “the power keeps going off”. The actual cause can vary, so it should be investigated properly rather than guessed.

When an Electrician Is Needed

You should arrange an electrician if:

The RCD trips immediately
The RCD keeps tripping randomly
The fault happens during wet weather
The fault affects more than one circuit
The RCD trips when fixed equipment is used
There are signs of burning, overheating or damage
The fault remains after appliances are unplugged
The consumer unit is old or damaged
The property is rented and tenants are affected

An electrician can carry out proper testing using calibrated equipment. This may include insulation resistance testing, RCD testing, earth fault testing, polarity checks and inspection of the affected circuits and accessories.

The aim is to find the actual cause of the fault, not just get the RCD to stay on temporarily.

RCD Faults and EICRs

An RCD fault may also come up during an EICR.

During an Electrical Installation Condition Report, the electrician checks the fixed electrical installation. This can include testing RCD operation, checking circuit condition, inspecting the consumer unit, checking bonding and earthing, and identifying signs of damage or deterioration.

If an RCD does not trip within the required time, or if testing identifies a fault on the fixed wiring, it may be recorded on the report. The observation will be coded depending on the risk and the specific finding.

A faulty plug-in appliance is different from a fault on the fixed installation. However, repeated RCD tripping should still be taken seriously, especially in rental properties.

Need Help With an RCD Fault?

EICR Pro carries out fixed-price EICR testing in London and can also help with fault finding where an RCD keeps tripping.

If the problem is linked to the fixed electrical installation, we can test the affected circuits, identify the likely cause and provide a clear quotation for any remedial work required.

Repeated RCD tripping should not be ignored. It may be something simple, but it can also be a sign of a fault that needs proper investigation.